Magnetic disk unit

Abstract: A magnetic disk unit comprises a rotor (9), on which a magnetic disk (18) is mounted, and which is integrally formed with a sleeve portion (10) of a ball bearing unit, or with a spindle (5) of a spindle motor for driving the disk, or with an inner or an outer race of the ball bearing unit in a disk drive unit of the magnetic disk unit, so that the need for alignment of the rotor with respect to the rotary axis of the ball bearing unit is eliminated in assembly of the magnetic disk unit and the rotor (9) is free from radial vibrations in operation whereby the recording density and reliability of the disk unit can be improved and whereby the number of parts of the magnetic disk unit and the number of assembly steps are reduced. Consequently the manufacturing cost of the magnetic disk unit is reduced as compared with known units.

Description: THE PRESENT INVENTION relates mainly to a magnetic disk unit employed in office automation instruments. In a conventional disk drive unit of the magnetic disk unit, as shown in Figure 12, a rotor on which a magnetic disk is mounted is rotatably driven by a motor which is generally constructed as a spindle motor. The spindle motor has a spindle mounted in a ball bearing unit to prevent the rotor's axial and radial vibrations. In the ball bearing unit, the spindle is mounted in a sleeve through a radial ball bearing constructed of an inner and an outer race, and a plurality of balls disposed between these races. In the conventional disk drive unit, the ball bearing unit and the rotor are separately constructed from each other, which increases the number of parts and the number of assembly steps required. Furthermore, in such assembly steps, it is necessary to mount the spindle on the rotor and to align the sleeve with a center of the ball bearing unit. Furthermore, such alignment of the sleeve must be performed in a precise manner. Also required to prevent the axial and radial vibrations of the rotor are highly developed technologies. These requirements increase production costs of the magnetic disk unit. In addition, in the conventional spindle motor of the disk drive unit the motor parts are separately constructed from the ball bearing unit. Consequently, also in this respect the number of parts and the number of assembly steps are increased in the conventional disk drive unit. In addition, in assembly of the disk drive unit, the alignment or centering of the motor parts with respect to the rotary axis of the ball bearing unit must be performed in a precise manner. These requirements increase manufacturing costs of the magnetic disk unit. EP-A-0425312 discloses a magnetic disk unit (disk drive) in which a rotor carrying a magnetic disk is mounted on a stationary spindle through the intermediary of two ball bearings each comprising an inner race secured to the spindle and an outer race fitted within a sleeve-like portion of the rotor hub. This prior art is reflected by the preamble of claim 1. JP-A-4265652 discloses a disk drive in which a rotor has an integral spindle extending within a sleeve-like portion of the drive casing, the rotor being rotatably mounted by means of two ball bearings acting between the spindle and the sleeve portion, each ball bearing including an inner race secured to the spindle and an outer race secured within the sleeve portion. This prior art is reflected by the preamble of Claim 4. WO-A-91/19344 discloses a disk drive in which a rotor, carrying the disks, is secured to a spindle, rotatably supported, by way of ball bearings, in a bearing housing bonded to a casing base of the disk drive. Each ball bearing comprises an inner race fitted on the spindle and a outer race fitted within the bearing housing. US-A-5138209 discloses a disk drive in which a sleeve-like rotor hub is rotatably mounted on a spindle fixedly mounted in the drive casing by way of two ball bearings, each comprising an inner race secured to the spindle and an outer race fitted within the sleeve-like hub. It is an object of the present invention to provide a magnetic disk unit provided with a precise disk drive unit in which a part of a ball bearing unit is integrally formed with a rotor of the disk drive unit to facilitate assembly of the disk unit, which reduces manufacturing costs of the disk unit. It is another object of the present invention to provide a magnetic disk unit provided with a precise disk drive unit in which a part of a disk drive motor is integrally formed with a sleeve portion of a main body of a ball bearing unit, or with a spindle of a motor, or with an inner or an outer race of the ball bearing unit to facilitate assembling works of the disk unit, which reduces manufacturing costs of the disk unit. According to one aspect of the present invention, there is provided a magnetic disk unit comprising a disk drive unit in which a motor on which a magnetic disk is mounted is rotatably driven by a rotor provided with a spindle which is mounted in a ball bearing unit which comprises a sleeve portion concentrically surrounding said spindle and a radial ball bearing disposed inside said sleeve portion, said sleeve portion of said ball bearing unit being integrally formed with said rotor, characterised in that said spindle is a stepped shaft comprising a large-diameter shaft portion and a small-diameter shaft portion; a ball-running groove is directly formed on an outer peripheral surface of said large-diameter shaft portion and said small-diameter shaft portion is fitted in an inner race; said sleeve portion has two ball-running grooves, which are directly formed in an inner peripheral surface; a plurality of balls is disposed between a ball-running groove of an outer peripheral surface of said inner race and a first one of said ball-running grooves of said sleeve portion and a plurality of balls is disposed between said ball-running groove of said large-diameter shaft portion and the second of said ball-running grooves of said sleeve portion. According to another aspect of the invention, there is provided a magnetic disk unit comprising a disk drive unit in which a rotor on which a magnetic disk is mounted is rotatably driven by a motor provided with a spindle which is mounted in a ball bearing unit which comprises a sleeve portion concentrically surrounding said spindle and a radial ball bearing disposed inside said sleeve portion, said spindle of said motor being integrally formed with said rotor, characterised in that said spindle is a stepped shaft comprising a large-diameter shaft portion and a small-diameter shaft portion; a ball-running groove is directly formed on an outer peripheral surface of said large-diameter shaft portion and said small-diameter shaft portion is fitted in an inner race; said sleeve portion has two ball-running grooves which are directly formed in an inner peripheral surface; a plurality of balls is disposed between a ball-running groove of an outer peripheral surface of said inner race and a first one of said ball-running grooves of said sleeve portion and a plurality of balls is disposed between said ball-running groove of said large-diameter shaft portion and the second of said ball-running grooves of said sleeve portion. Preferably the sleeve portion or the spindle formed integrally with the rotor is formed in a central portion of a lower surface of the rotor through a molding process. As is clear from the above, in various embodiments, the rotor is integrally formed with the sleeve portion of the ball bearing unit, or with the spindle of the motor. In the accompanying drawings:- Fig. 1 is a partially exploded perspective view of a magnetic disk unit of the present invention; Fig. 2 is a longitudinal sectional view of a first embodiment of the disk drive unit of the magnetic disk unit of the present invention; Fig. 3 is a longitudinal sectional view of a second embodiment of the disk drive unit of the magnetic disk unit of the present invention; Fig. 4 is a longitudinal sectional view of a third embodiment of the disk drive unit of the magnetic disk unit of the present invention; Fig. 5 is a longitudinal sectional view of a fourth embodiment of the disk drive unit of the magnetic disk unit of the present invention; Fig. 6 is a longitudinal sectional view of an embodiment of the disk drive unit of the magnetic disk unit of the present invention, in which the sleeve portion of the ball bearing unit is integrally formed with the rotor of the disk drive unit; Fig. 7 is a longitudinal sectional view of a disk drive unit, in which the sleeve portion of the ball bearing unit is also integrally formed with the rotor of the disk drive unit; Fig. 8 is a longitudinal sectional view of another disk drive unit, in which the sleeve portion of the ball bearing unit is also integrally formed with the rotor of the disk drive unit; Fig. 9 is a longitudinal sectional view of an embodiment of the disk drive unit of the magnetic disk unit of the present invention, in which the sleeve portion of the ball bearing unit is integrally formed with the yoke holder of the motor of the disk drive unit; Fig. 10 is a longitudinal sectional view of an embodiment of the disk drive unit of the magnetic disk unit of the present invention, in which the inner race of the ball bearing unit is integrally formed with the yoke holder of the motor of the disk drive unit; Fig. 11 is a longitudinal sectional view of an embodiment of the disk drive unit of the magnetic disk unit of the present invention, in which the spindle of the ball bearing unit is integrally formed with the yoke holder of the motor of the disk drive unit; and Fig. 12 is a longitudinal sectional view of a conventional disk drive unit of a magnetic disk unit. Hereinbelow, the present invention will be described in. detail with reference to embodiments of a magnetic disk unit of the present invention shown in the accompanying drawings. Fig. 1 is a partially exploded perspective view of a first embodiment of a magnetic disk unit of the present invention, the disk unit employing an outer-rotor type spindle motor M which belongs to the applicant's company of the subject application. Fig. 2 is a longitudinal sectional view of a disk drive unit 22 of the magnetic disk unit of the present invention. In Figs. 1 and 2, the reference numeral 1 denotes a casing of the magnetic disk unit. The casing 1 is provided with the outer-rotor type spindle motor M which has the following construction. Namely, a sleeve-like yoke holder 2 provided with a bottom portion is mounted on a base portion la of the casing 1. Disposed around the yoke holder 2 is a stator yoke 4 which is wound with an energizing coil 3. A spindle 5 has its lower portion fixedly mounted in a center hole of the bottom portion of the yoke holder 2 and has its upper portion formed into a small-diameter shaft portion, so that the spindle 5 is constructed of a lower large-diameter shaft portion and the upper small-diameter shaft portion to form a stepped shaft. Formed in an outer peripheral portion of the lower large-diameter shaft portion of the spindle 5 is a ball-running groove 6. An inner race 8 of the ball bearing unit is fitted to the small-diameter shaft portion of the spindle 5, and provided with a ball-running groove 7 in its outer peripheral portion. A sleeve portion 10 for a main body of a ball bearing unit is integrally formed with a rotor 9 and extends downward from a lower surface of a central portion of the rotor 9 on which a magnetic disk 18 is loaded. Formed in an inner surface of the sleeve portion 10 of the rotor 9 are a pair of ball-running grooves 11 and 12 which are oppositely disposed from the ball-running grooves 6 and 7, respectively. The ball-running groove 6 is of the large-diameter shaft portion of the spindle 5, while the ball-running groove 7 is of the inner race 8 of the ball bearing unit. A plurality of balls 13 are disposed between the ball-running grooves 6 and 11, while a plurality of balls 14 are disposed between the ball-running grooves 7 and 12. As is clear from the above description, the main body of the ball bearing unit is constructed of the sleeve portion 10 of the rotor 9, balls 13 and 14 and the ball-running grooves 6 and 7 so that the rotor 9 is rotatably mounted on the spindle 5. Incidentally, in the drawings, the reference numeral 15 denotes a magnet which is mounted on an inner surface of a flange portion 9a of the rotor 9 so as to be oppositely disposed from the stator yoke 4. The disk drive unit of this embodiment is characterized in that the sleeve portion 10 of the main body of the ball bearing unit is integrally formed with the rotor 9. In the disk drive unit 22 of a second embodiment of the present invention shown in Fig. 3, the sleeve portion 10 of the main body of the ball bearing unit is provided in the central portion of the base portion 1a of the casing 1. The spindle 5 is integrally formed with the rotor 9 so as to extend downward from a lower surface of the central portion of the rotor 9. As is clear from Fig. 3, the spindle 5 of the second embodiment is provided with an upper large-diameter shaft portion and a lower small-diameter shaft portion to form a stepped shaft, which is reverse in arrangement to that of the first embodiment shown in Fig. 2. However, as is in the second embodiment shown in Fig. 2, in the ball bearing unit: the ball-running groove 6 of the spindle 5 and the ball-running groove 7 of the inner race 8 of the bearing unit are oppositely disposed from the ball-running grooves 11 and 12 of the sleeve portion 10 of the bearing unit, respectively; and, the balls 13 and 14 are disposed between these ball-running grooves in the same manner as that of the second embodiment. In this second embodiment of the present invention, as shown in Fig. 3, the stator yoke 4 is mounted on an outer peripheral portion of the sleeve portion 10 of the bearing unit so that the yoke holder 2 of the first embodiment shown in Fig. 2 is eliminated in construction. The second embodiment of the present invention shown in Fig. 3 is characterized in that the spindle 5 of the main body of the ball bearing unit is integrally formed with the rotor 9. Figs. 4 and 5 show a third and a fourth embodiment of the present invention, respectively. In each of these embodiments, the drive motor is constructed of an inner-rotor type spindle motor. In the third embodiment of the present invention shown in Fig. 4, the spindle 5 constructed of a stepped shaft is mounted in a central hole of a bottom portion of the stator yoke holder 2 so as to extend upward from the bottom portion of the holder 2 which is provided with a sleeve-like rib portion 2a. The stator yoke 4 is mounted on an inner peripheral surface of the rib portion 2a of the stator yoke holder 2. The disk drive unit of the third embodiment of the present invention shown in Fig. 4 is characterized in that the sleeve portion 10 of the main body of the ball bearing unit is integrally formed with the rotor 9 in the lower surface of the central portion of the rotor 9. The remaining construction of the main body of the ball bearing unit of the third embodiment shown in Fig. 4 is the same as that of the main body of the ball bearing unit of the first embodiment shown in Fig. 2, with the exception of the magnet 15 which is mounted on the outer peripheral portion of the sleeve portion 10 of the ball bearing unit in the third embodiment as shown in Fig. 4. The fourth embodiment of the disk drive unit shown in Fig. 5 is characterized in that: the stator yoke holder 2 of the motor is integrally formed with the sleeve portion 10 of the main body of the ball bearing unit; and, the spindle 5 is integrally formed with the rotor 9. In the fourth embodiment shown in Fig. 5: the stator yoke 4 is mounted on the inner peripheral surface of the rib portion 2a of the holder 2; and, the magnet 15 is mounted on an outer peripheral portion of a sleeve-like magnet holder 16 which is integrally formed with the rotor 9 so as to extend downward from the lower surface of the central portion of the rotor 9. In the fourth embodiment shown in Fig. 5: the spindle 5 is constructed of a stepped shaft; and, there is no difference in construction of the main body of the ball bearing unit between the fourth embodiment shown in Fig. 5 and the second embodiment shown in Fig. 3. Incidentally, in Fig. 1: the reference numeral 19 denotes a magnetic head provided in a lower surface of a front-end portion of a head arm 20; and the reference numeral 21 denotes an upper lid of the unit. In each of the above embodiments of the present invention, though a printed circuit board connected with the coil 3 for actuating the drive motor M is mounted on an inner (or an upper) surface of the base portion la of the casing 1, such printed circuit board is omitted in the drawings to clarify the essential parts of the present invention. Further embodiments of the present invention, will be described in construction, as follows. Fig. 6 shows an embodiment of the present invention, in which embodiment the sleeve portion 10 of the main body of the ball bearing unit is integrally formed with the rotor 9 of the disk drive unit. Figs. 7 and 8 shows other disk drive units. Fig. 9 shows another embodiment in which the sleeve portion 10 of the main body of the ball bearing unit is integrally formed with the yoke holder 2 of the drive motor M. Fig. 10 shows further another embodiment of the present invention, in which the inner race 8 of the main body of the ball bearing unit is integrally formed with the yoke holder 2 of the drive motor M. Fig. 11 shows still further- another embodiment of the present invention, in which the spindle 5 of the ball bearing unit is integrally formed with the yoke holder 2 of the drive motor M. In the disk drive unit of the magnetic disk unit of. the present invention, the main body of the ball bearing unit has its spindle or inner race or outer race formed integrally with the rotor or the yoke holder of the drive motor. Consequently, in contrast with the conventional drive unit in which a part of the ball bearing unit and the rotor or the yoke holder are separately constructed from each other, the disk drive unit of the present invention is improved in easiness in assembly, and, therefore reduces its manufacturing costs, which are the advantages of the present invention over the prior art. Further, since the main body of the ball bearing unit has its sleeve portion or spindle or inner race or outer race formed integrally with an adequate part of the rotor or the yoke holder, it is possible to eliminate cumbersome alignment works of the spindle with the above parts in assembling works of the disk drive unit, which makes it possible to substantially eliminate the radial vibrations of the spindle in the disk drive unit of the present invention, which enables the disk drive unit of the present invention to be a precise unit. Consequently, according to the present invention, it is possible to improve the magnetic disk unit in reliability in data transmission between the magnetic disk and the magnetic head, which makes it possible to improve the magnetic disk in track density. In addition, in the magnetic disk unit of the present invention, since the magnetic disk is substantially not axially vibrated, it is possible to minimize a clearance between the magnetic head and the magnetic disk, which makes it possible to improve the magnetic disk in track recording density. As a result, it is possible for the present invention to provide the magnetic disk unit excellent in reliability and track recording density. In each of the above-described embodiments, the rotor 9, and the parts described or shown as being integral with the rotor, are preferably formed integrally by a moulding process.

Claims: A magnetic disk unit comprising a disk drive unit (22) in which a rotor (9) on which a magnetic disk (18) is mounted is rotatably driven by a motor provided with a spindle (5) which is mounted in a ball bearing unit which comprises a sleeve portion (10) concentrically surrounding said spindle and a radial ball bearing disposed inside said sleeve portion (10), said sleeve portion (10) of said ball bearing unit being integrally formed with said rotor (9), characterised in that said spindle (5) is a stepped shaft comprising a large-diameter shaft portion and a small-diameter shaft portion; a ball-running groove (6) is directly formed on an outer peripheral surface of said large-diameter shaft portion and said small-diameter shaft portion is fitted in an inner race (8); said sleeve portion (10) has two ball-running grooves (12), (11) which are directly formed in an inner peripheral surface; a plurality of balls (14) is disposed between a ball-running groove (7) of an outer peripheral surface of said inner race and a first (12) one of said ball-running grooves of said sleeve portion (10) and a plurality of balls (13) is disposed between said ball-running groove (6) of said large-diameter shaft portion and the second (11) of said ball-running grooves of said sleeve portion (10). A magnetic disk unit according to claim 1 wherein a yoke holder (2) for concentrically surrounding said sleeve portion is provided in a base portion (1a) of a casing (1); a stator yoke (4) provided with an energizing coil (3) is provided in an outer peripheral portion of said yoke holder (2), and a magnet (15) is provided in an inner peripheral surface of a flange portion of said rotor (9). A magnetic disk unit according to claim I wherein a magnet (15) is provided in an outer peripheral surface of said sleeve portion (10); a sleeve-like yoke holder (2a) surrounding said magnet is concentrically arranged with respect to said spindle so as to be provided in a base portion (1a) of a casing (1), and a stator yoke (4) provided with an energizing coil (3) is provided in an inner peripheral surface of said yoke holder (2a). A magnetic disk unit comprising a disk drive unit (22) in which a rotor (9) on which a magnetic disk (18) is mounted is rotatably driven by a motor provided with a spindle (5) which is mounted in a ball bearing unit which comprises a sleeve portion (10) concentrically surrounding said spindle and a radial ball bearing disposed inside said sleeve portion (10), said spindle (5) of said motor being integrally formed with said rotor (9), characterised in that said spindle (5) is a stepped shaft comprising a large-diameter shaft portion and a small-diameter shaft portion; a ball-running groove (6) is directly formed on an outer peripheral surface of said large-diameter shaft portion and said small-diameter shaft portion is fitted in an inner race (8); said sleeve portion (10) has two ball-running grooves (12) (11) which are directly formed in an inner peripheral surface; a plurality of balls (14) is disposed between a ball-running groove (7) of an outer peripheral surface of said inner race and a first (12) one of said ball-running grooves of said sleeve portion (10) and a plurality of balls (13) is disposed between said ball-running groove (6) of said large-diameter shaft portion and the second (11) of said ball-running grooves of said sleeve portion (10). A magnetic disk unit according to claim 4 wherein said sleeve portion (10) is provided in said base portion (1a) of said casing (1); a stator yoke (4) provided with an energizing coil (3) is provided in an outer peripheral surface of said sleeve portion to make it possible that said sleeve portion also serves as a yoke holder; and a magnet (15) is provided in an inner peripheral surface of a flange portion of said rotor. A magnetic disk unit according to claim 4, wherein a magnet holder (16) which is coaxially arranged with said spindle is integrally formed with said rotor, a magnet (15) is provided in an outer peripheral surface of said magnet holder; a yoke holder (2a) surrounding said magnet is coaxially arranged with said spindle; and a stator yoke (4) provided with an energizing coil (3) is provided in an inner peripheral surface of said yoke holder. A magnetic disk unit according to claim 1 wherein said inner race (8) is formed integrally with a yoke holder (2) of said motor.

Inventors: OBARA RIKURO, OBARA, RIKURO
Applicants: MINEBEA KK, MINEBEA KABUSHIKI-KAISHA
Application year: 1994
Main classification: G11B19
IPC codes: G11B25, G11B19